1. Field of the Invention
The present invention relates to a method of and apparatus for preventing overheating of various types of heating elements such as motors and print heads, etc., for use in terminal units of all sorts for protection thereof.
2. Description of the Prior Art
Printers are well known as terminal units. Such a printer includes a line feed motor (hereinafter, referred to simply as an LF motor) for feeding a printing paper for its new line, a spacing motor for moving a print head horizontally, and the print head, all being mounted thereon and regarded as heating elements.
For example, in case of the LF motor, continuous line feed operation thereof over a long period of time causes temperature of windings of the motor to be abnormally raised to result in the baking thereof and the deterioration of the performance thereof. Prior methods solved such problems as follows:
1 A large rating motor is employed, or the temperature of a motor is prevented from rising over a rated value thereof even if it is rendered to continuous line feed using radiating fins mounted thereon.
2 An operator's attention is called to an operating manual of a printer specifying that continuous line feed over a long period of time should not be done.
3 As disclosed in Japanese Laid-Open Patent Publication No. 57-11041, a heat sensitive element is used to determine whether or not the temperature of a heating element exceeds an allowable value. If it exceeds that value, then a required pause time interval is placed in a drive period of driving power applied to the heating element to permit heat dissipation to be effected during that pause time interval.
However, those methods to solve the aforementioned difficulties respectively suffered from the following problems:
The countermeasure 1 exerts itself for continuous operation for many hours not experienced in ordinary applications, which can never be said to be effective to result in the device cost increased. The countermeasure 2 can not prevent a motor from being overheated when an operator does not obey directions of the device for use and when there is any trouble in a host computer connected to a printer. Furthermore, the countermeasure 3 necessitates a heat sensitive element to result in the apparatus cost increased.